Since the discovery of X-rays by Roentgen, X-ray based CT imaging technology has developed rapidly and is widely used in medical imaging and security inspection. At present, detectors applied for X-ray imaging mainly employ the following two methods for signal acquisition: energy integration and photon counting. In recent years, due to advantages of multi-spectral imaging in discrimination of material compositions or the like, a photon counting detector has become a research hotspot in related fields. There are several research institutes and companies in the world dedicated to research and production of photon counting detectors for X-ray imaging. The photon counting detector counts photons with distinct energy according to the energy of the individual photons passing through an object. In this way, low-energy photons can be filtered out by setting a threshold to reduce noise and radiation. At the same time, by setting a plurality of thresholds, the counting for X-rays with a wide energy spectrum distribution can be performed per energy regions, and imaging results of different energy regions can be directly obtained. Compared with an energy integration detector, the photon counting detector can eliminate influence of low-energy noise on the imaging and improve image quality. On the other hand, the photon counting detector can distinguish the energy more precisely and reduce correlation among data acquired for X-ray imaging. Thus, the X-ray imaging by the photon counting detector can improve accuracy of material discrimination, precision of component quantization, and the like.
The photon counting detector plays an increasingly important role in the X-ray imaging. However, it has a high cost. On the other hand, the photon counting detector is greatly limited by the counting rate and the number of energy window channels, and accordingly it is hard to optimize efficiency of data acquisition. In an ideal case, X-ray photons of different energy carry different information. If different photons can be subdivided referring to sufficient energy intervals and processed differently according to their individual energy, the image quality can be optimized to the greatest extent. The above two signal acquisition methods applied to X-ray imaging detectors correspond to two “energy-weighted” signal processing methods: the energy integration detector uses energy as a weight to perform a weighted accumulation of all photon signals to obtain an output; the photon counting detector performs a weighted accumulation of the individual photons with a constant as a weight in a specified energy range to obtain an output. No signal optimization strategy can be used for the output of each of these two detectors. Thus the image quality of CT imaging systems based on them is necessarily limited.